Multifactorial genetic models for the natural history of alcohol use and abuse across the life-span, in clinically unselected, untreated populations, will be developed and refined by computer simulation and theoretical analysis. The utility of family- structured survey designs (e.g. adoption or twin family designs) for resolving the joint effects of genetic liability and environmental risk factors, and their covariation and interaction, will be explored by computer simulation and power calculations. Current controversies about the heterogeneity of alcohol abuse and its causes, and about the direction of causal pathways linking alcohol abuse and personality and environmental variables, will be addressed. Specific hypotheses will be tested, initially, using three existing sets of familial data on alcohol use and abuse: (i) 3810 adult twin pairs, aged 18-88, from the Australian twin panel; (ii) 2500 adult twin pairs, aged 16-71, and their parents (N=2000), siblings (N=2500) and spouses (N=2500), from the Virginia twin register; (iii) 3000 adult twin pairs aged 50-95, and their siblings (N=1500), spouses (N=2500). The sex- and age-structure of these samples will allow detailed analysis of two special populations: women; and the elderly. Modelling and, where possible, data analysis, will address: (i) genetic and environmental factors determining the onset and course of teenage alcohol use, including the role of peer selection and peer effects; (ii) the interactions which occur between onset of smoking, onset of alcohol use, and other substance abuse; (iii) the role of personality traits (e.g. extraversion, neuroticism, impulsivity) and of sociocultural characteristics (e.g. religious affiliation) as stable mediators of, respectively, genetic and familial environmental effects on patterns of alcohol use: (iv) the effects of cohort-related sociocultural changes, and changes in the social environment (leaving home; marriage; parenthood; separation; bereavement) on the course of drinking habits, and their interaction with genetic differences; (v) the multivariate structure of genetic and environmental determinants of alcohol use and abuse; (vi) the developmental course of alcohol use and abuse across the life span.